On Fri, Mar 22, 2024 at 12:58:17PM +0000, Jonathan Cameron wrote: > On Fri, 22 Mar 2024 16:09:35 +0530 > 'Manivannan Sadhasivam' <manivannan.sadhasivam@xxxxxxxxxx> wrote: > > > On Wed, Mar 20, 2024 at 10:01:44AM +0000, Jonathan Cameron wrote: > > > On Tue, 19 Mar 2024 22:03:15 +0530 > > > 'Manivannan Sadhasivam' <manivannan.sadhasivam@xxxxxxxxxx> wrote: > > > > > > > On Thu, Feb 22, 2024 at 04:30:47PM +0530, Shradha Todi wrote: > > > > > + Borislav, Tony, James, Mauro, Robert > > > > > > > > > > Hi All, > > > > > > > > > > Synopsys DesignWare PCIe controllers have a vendor specific capability (which > > > > > means that this set of registers are only present in DesignWare controllers) > > > > > to perform debug operations called "RASDES". > > > > > The functionalities provided by this extended capability are: > > > > > > > > > > 1. Debug: This has some debug related diagnostic features like holding LTSSM > > > > > in certain states, reading the status of lane detection, checking if any PCIe > > > > > lanes are broken (RX Valid) and so on. It's a debug only feature used for diagnostic > > > > > use-cases. > > > > > > > > > > 2. Error Injection: This is a way to inject certain errors in PCIe like LCRC, ECRC, > > > > > Bad TLPs and so on. Again, this is a debug feature and generally not used in > > > > > functional use-case. > > > > > > > > > > 3. Statistical counters: This has 3 parts > > > > > - Error counters > > > > > - Non error counters (covered as part of perf [1]) > > > > > - Time based analysis counters (covered as part of perf [1]) > > > > > > > > > > Selective features of the above functionality has been implemented > > > > > by vendor specific PCIe controller drivers (pcie-tegra194.c) that use > > > > > Synopsys DesignWare PCIe controllers. > > > > > In order to make it useful to all vendors using DWC controller, we had > > > > > proposed a common implementation in DWC PCIe controller directory > > > > > (drivers/pci/controller/dwc/) and our original idea was based on debugfs > > > > > filesystem. v1 and v2 are mentioned in [2] and [3]. > > > > > > > > > > We got a suggestion to implement this as part of EDAC framework [3] and > > > > > we looked into the same. But as far as I understood, what I am trying to > > > > > implement is a very specific feature (only valid for Synopsys DWC PCIe controllers). > > > > > > For error part there are (at least superficially) similar features in the PCIe > > > standard that we've started thinking about how to support. > > > > > > See Flit Logging Extended capablity (7.7.8 in PCIe Base Spec rev6. > > > That has the benefit that they are part of the standard so we can > > > support them directly in portdrv / EP drivers using some library code in the > > > PCI core. > > > > > > > Sounds good. But v6 is a relatively new version and the DWC RAS predates that. > > So we still need to support it somehow (either in EDAC or in > > drivers/pci/controller/dwc). > > > > > There are other interconnect and PCI PMU drivers that log retries etc which are also basically error > > > counts. At least some of that is done through perf today. > > > > > > > IMO all the RAS support should be exposed through EDAC, otherwise it defeats the > > purpose of the subsystem. > > Some RAS flows go nowhere near EDAC today. Individual drivers poke out > the tracepoints and userspace tooling deals with it. One example is > CXL but there are plenty of others. > That's the problem. You'd end up with custom tooling for each individual drivers leading to userspace fragmentation. - Mani > Perhaps that should not be the case, but there is definitely > precedence for ignoring edac when considering error flows. > > Jonathan > > > > > - Mani > > > > > > > > > > This doesn't seem to fit in very well with the EDAC framework and we can > > > > > hardly use any of the EDAC framework APIs. We tried implementing a > > > > > "pci_driver" but since a function driver will already be running on the EP and > > > > > portdrv on the root-complex, we will not be able to bind 2 drivers to a single > > > > > PCI device (root-complex or endpoint). Ultimately, what I will be doing is > > > > > writing a platform driver with debugfs entries which will be present in EDAC > > > > > directory instead of DWC directory. > > > > > > The addition of this type of functionality to pordrv is a long running question. > > > Everyone wants a solution, I believe some people are looking at it (+CC Terry) > > > > > > Terry, another case for your long list. > > > > > > For the EP end, this should be fired up by the EP driver, whilst it might be > > > infrastructure used on a bunch of devices, it is a feature of that particular > > > EP - so you'd want to provide any functionality in a form that could be used > > > by both the EP driver and a nice shiny new portdrv replacement. > > > > > > > > > > > > > Can you please help us out by going through this thread [3] and letting us > > > > > know if our understanding is wrong at any point. If you think it is a better > > > > > idea to integrate this in the EDAC framework, can you guide me as > > > > > to how I can utilize the framework better? > > > > > Please let me know if you need any other information to conclude. > > > > > > > > > > [1] https://lore.kernel.org/linux-pci/20231121013400.18367-1-xueshuai@xxxxxxxxxxxxxxxxx/ > > > > > [2] https://lore.kernel.org/all/20210518174618.42089-1-shradha.t@xxxxxxxxxxx/T/ > > > > > [3] https://lore.kernel.org/all/20231130115044.53512-1-shradha.t@xxxxxxxxxxx/ > > > > > > > > > > > > > Gentle ping for the EDAC maintainers. > > > > > > > > - Mani > > > > > > > > > Thanks, > > > > > Shradha > > > > > > > > > > > -----Original Message----- > > > > > > From: 'Manivannan Sadhasivam' <manivannan.sadhasivam@xxxxxxxxxx> > > > > > > Sent: 16 February 2024 19:19 > > > > > > To: Shradha Todi <shradha.t@xxxxxxxxxxx> > > > > > > Cc: lpieralisi@xxxxxxxxxx; kw@xxxxxxxxx; robh@xxxxxxxxxx; > > > > > > bhelgaas@xxxxxxxxxx; jingoohan1@xxxxxxxxx; > > > > > > gustavo.pimentel@xxxxxxxxxxxx; josh@xxxxxxxxxxxxxxxx; > > > > > > lukas.bulwahn@xxxxxxxxx; hongxing.zhu@xxxxxxx; > > > > > > pankaj.dubey@xxxxxxxxxxx; linux-kernel@xxxxxxxxxxxxxxx; linux- > > > > > > pci@xxxxxxxxxxxxxxx; vidyas@xxxxxxxxxx; gost.dev@xxxxxxxxxxx > > > > > > Subject: Re: [PATCH v2 0/3] Add support for RAS DES feature in PCIe DW > > > > > > controller > > > > > > > > > > > > On Thu, Feb 15, 2024 at 02:55:06PM +0530, Shradha Todi wrote: > > > > > > > > > > > > > > > > > > > > > > > > > > [...] > > > > > > > > > > > > > > For the error injection and counters, we already have the EDAC > > > > > > > > framework. So adding them in the DWC driver doesn't make sense to me. > > > > > > > > > > > > > > > > > > > > > > Sorry for late response, was going through the EDAC framework to understand > > > > > > better how we can fit RAS DES support in it. Below are some technical challenges > > > > > > found so far: > > > > > > > 1: This debugfs framework proposed [1] can run on both side of the link i.e. RC > > > > > > and EP as it will be a part of the link controller platform driver. Here for the EP > > > > > > side the assumption is that it has Linux running, which is primarily a use case for > > > > > > chip-to-chip communication. After your suggestion to migrate to EDAC > > > > > > framework we studied and here are the findings: > > > > > > > - If we move to EDAC framework, we need to have RAS DES as a > > > > > > > pci_driver which will be binded based on vendor_id and device_id. Our > > > > > > > observation is that on EP side system we are unable to bind two > > > > > > > function driver (pci_driver), as pci_endpoint_test function driver or > > > > > > > some other chip-to-chip function driver will already be bound. On the > > > > > > > other hand, on RC side we observed that if we have portdrv enabled in > > > > > > > Linux running on RC system, it gets bound to RC controller and then it > > > > > > > does not allow EDAC pci_driver to bind. So basically we see a problem > > > > > > > here, that we can't have two pci_driver binding to same PCI device > > > > > > > 2: Another point is even though we use EDAC driver framework, we may not be > > > > > > able to use any of EDAC framework APIs as they are mostly suitable for memory > > > > > > controller devices sitting on PCI BUS. We will end up using debugfs entries just via > > > > > > a pci_driver placed inside EDAC framework. > > > > > > > > > > > > Please wrap your replies to 80 characters. > > > > > > > > > > > > There is no need to bind the edac driver to VID:PID of the device. The edac driver > > > > > > can be a platform driver and you can instantiate the platform device from the > > > > > > DWC driver. This way, the PCI device can be assocaited with whatever driver, but > > > > > > still there can be a separate edac driver for handling errors. > > > > > > > > > > > > Regarding API limitation, you should ask the maintainer about the possibility of > > > > > > extending them. > > > > > > > > > > > > > > > > > > > > Please let me know if my understanding is wrong. > > > > > > > > > > > > > > > But first check with the perf driver author if they have any plans > > > > > > > > on adding the proposed functionality. If they do not have any plan > > > > > > > > or not working on it, then look into EDAC. > > > > > > > > > > > > > > > > - Mani > > > > > > > > > > > > > > > > > > > > > > Since we already worked and posted patches [1], [2], we will continue to work > > > > > > on this and based on consent from community we will adopt to most suitable > > > > > > framework. > > > > > > > We see many subsystems like ethernet, usb, gpu, cxl having debugfs files that > > > > > > give information about the current status of the running system and as of now > > > > > > based on our findings, we still feel there is no harm in having debugfs entry based > > > > > > support in DesignWare controller driver itself. > > > > > > > > > > > > There is no issue in exposing the debug information through debugfs, that's the > > > > > > sole purpose of the interface. But here, you are trying to add support for DWC > > > > > > RAS feature for which a dedicated framework already exists. > > > > > > > > > > > > And there will be more similar requests coming for vendor specific error protocols > > > > > > as well. So your investigation could benefit everyone. > > > > > > > > > > > > From your above investigation, looks like there are some shortcomings of the > > > > > > EDAC framework. So let's get that clarified by writing to the EDAC maintainers > > > > > > (keep us in CC). If the EDAC maintainer suggests you to add support for this > > > > > > feature in DWC driver itself citing some reasons, then no issues with me. > > > > > > > > > > > > - Mani > > > > > > > > > > > > -- > > > > > > மணிவண்ணன் சதாசிவம் > > > > > > > > > > > > > > > > > > > > -- மணிவண்ணன் சதாசிவம்
